this is a lovely idea! i see giving coins as tokens to your best friends - i myself have a coin a friend gave me i carry as a good luck charm! also, wedding & party favors would be brilliant. and sites like GetGlue come to mind, where you get actual physical stickers for checking in - custom metal tokens/coins for super cool up and coming web sites/services, viral marketing & alternate reality gaming swag... yeah. i'm sorta into this idea ;)